Recent years have seen an increase in the number of applications for video on demand type services, such as video-conferencing through the Internet, digital video broadcasting, and streaming video content. These applications depend on transmission of video information. These applications require that such video data having a substantial amount of digital data is transmitted through conventional transmission channels having limited bandwidth or recorded on conventional recording media having limited data capacity. Accordingly, in order to transmit the video data using a conventional transmission channel or record the video data onto a conventional recording medium, compression or reduction of the amount of the video data is necessary.
Many video coding standards have been developed for the purpose of compressing video data. Such video coding standards include: International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Standard denoted as H. 26x; and International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Standard denoted as MPEG-x, for example. The latest and most advanced video coding standard to date is a standard denoted as H.264/AVC or MPEG-4 AVC (see Non-Patent Literature (NPL) 1).
In H.264/AVC Standard, information is compressed by: predicting an image signal based on an image signal that has already been coded and decoded; and coding prediction information and a residual signal which is obtained by transforming and quantizing a residual signal between an input image signal and the predicted image signal. In the prediction of the image signal, two reference picture lists L0 and L1 are used as information for identifying a picture that has already been coded and decoded (reference picture). As information for identifying the reference picture, the following are used: first information for identifying which one of the two reference picture lists L0 and L1 should be used; and second information for identifying the reference picture. For example, FIG. 18 shows a variable-length coding unit which variable-length codes the above first information and the second information, and FIG. 19 shows a variable-length decoding unit which variable-length decodes the first and second information.